Power charerstics are the same as a 500 small vs large reed, the small reed makes more bottom end and a smoother power band all the way through.  A ported set up to a ported set up, you won't see much difference on the 250 the small reed will pull a little harder before it really comes on the pipe,  where the large reed will be a little dead feeling if its ported the same untilled it comes on the pipe and makes a maybe a couple more HP.  I actually prefer the small reed in either the 500 or 250 for all around power and racing. If your drag and hill shooting only the 87 could be an advantage. In the 250 its not a noticeable difference up top until you radically port, even then its still not a clear advantage I've ever seen. On a big bore engine the 87 has potential to work more like the 500.